Manipulation of plants to alter and/or improve phenotypic characteristics (such as productivity or quality) requires the expression of heterologous genes in plant tissues. Such genetic manipulation relies on the availability of a means to drive and to control gene expression as required. For example, genetic manipulation relies on the availability and use of suitable promoters which are effective in plants and which regulate gene expression so as to give the desired effect(s) in the transgenic plant.
The seed-preferential or seed-specific promoters are useful for expressing genes as well as for producing large quantities of protein, for expressing oils or proteins of interest, e.g., antibodies, genes for increasing the nutritional value of the seed and the like. It is advantageous to have the choice of a variety of different promoters so that the most suitable promoter may be selected for a particular gene, construct, cell, tissue, plant or environment. Moreover, the increasing interest in cotransforming plants with multiple plant transcription units (PTU) and the potential problems associated with using common regulatory sequences for these purposes merit having a variety of promoter sequences available.
Only a few seed-specific promoters have been cloned and studied in detail; these include promoters for seed storage protein genes, such as a phaseolin promoter (U.S. Pat. No. 5,504,200) and a napin promoter (U.S. Pat. No. 5,608,152). Storage proteins are usually present in large amounts, making it relatively easy to isolate storage protein genes and the gene promoters. Even so, the number of available seed specific promoters is still limited. Furthermore, most of these promoters suffer from several drawbacks; they have a limited period of time during seed development in which they are active, and they may be expressed in other tissues as well. For example, storage protein gene promoters are expressed mainly in the mid to late embryo development stage (Chen et al., Dev. Genet., (2): 112-122 (1989); Keddie et al., Plant Mol. Biol., 19 (3): 443-53 (1992); Sjodahl et al., Planta., 197 (2): 264-71 (1995); Reidt et al., Plant J., 21 (5): 401-8 (2000)), and also may have activity in other tissues, such as pollen, stamen and/or anthers (as, for example, the phaseolin promoter, as reported by Ahm, V, et al. Plant Phys 109: 1151-1158 (1995)).
There is, therefore, a great need in the art for the identification of novel sequences that can be used for expression of selected transgenes in economically important plants. Thus, the problem underlying the present invention is to provide new and alternative expression cassettes for seed-preferential or seed-specific expression of transgenes in plants. The problem is solved by the present invention.